The present invention relates to a process for manufacturing anodized, colored aluminum.
Anodized aluminum is used in a variety of applications including building materials, household appliances, automotive trim, foil applications, farm equipment, furniture, sporting goods, and containers. Anodized aluminum products are desirable because they exhibit many beneficial functional characteristics such as: resistance to corrosion, chemical staining, and fading; electrical insulation; and exceptional structural rigidity.
Currently, most anodized aluminum is manufactured in two-sided sheet or coil form, where (1) both sides of the sheet or coil are anodized with a sulfuric acid anodizing process or (2) both sides of the sheet or coil are anodized with a phosphoric acid anodizing process. Sulfuric acid anodized aluminum is readily colored, and therefore is suitable for applications requiring a decorative finish. However, conventional sulfuric acid anodized aluminum is incompatible with most commercially available adhesives. Accordingly, it is difficult to adhere sheets of decoratively finished sulfuric acid anodized aluminum to other materials.
In contrast, phosphoric acid anodized aluminum satisfactorily bonds with commercially available adhesives, and thus is a good candidate for applications where anodized aluminum sheets must be adhered to other materials. However, phosphoric acid anodized aluminum is difficult to color. Accordingly, although the phosphoric acid anodized acid sheets are readily bonded with other materials, the color of the sheets is limited to a dull-grayish finish.
A drawback of conventional anodizing processes is that both sides of manufactured sheets and coils of anodized aluminum either exhibit the desirable decorative function of sulfuric anodized aluminum or exhibit the desirable enhanced adhesion characteristics of phosphoric acid anodized aluminum. As a result, in many applications of anodized aluminum, one must weigh the trade-off between the decorative function and the adhesion characteristics.